Why do some water features have a distinct ZCTA Code?
The requirements for ZCTA delineation state that all census blocks receive a ZCTA code. Because large water features may border many five-digit ZCTAs, it would be difficult to divide up the water features and assign the parts to the five-digit ZCTAs on the land. Furthermore, any attempt to add these water features to land-based ZCTAs, would greatly distort the size and shape of the land ZCTAs, particularly in coastal areas. To avoid these problems, such water features receive ZCTA codes ending in “HH” (special code for hydrographic features). Note that a single code could not be used for all water areas for data processing reasons.
